The overall goal of the proposed research is to use converging methods to better understand the causal relation between RD and its psychiatric correlates particularly ADHD. The specific goals of the proposed research are: 1. To administer measures of attention deficit hyperactivity disorder (ADHD) and executive functions (EFs) to three different populations; a) 50 pairs of MZ and 50 pairs of DZ twins in which at least one member of each pair is reading disabled (RD); b) an independent sample of 50 pairs of MZ and 50 pairs of DZ twins in which at least one member of each pair manifests symptoms of ADHD; and c) a comparison group of 50 pairs of MZ and 50 pairs of DZ twins with no school history of learning disabilities (LDs) or ADHD. 2. To perform a genetic linkage study to identify one or more quantitative trait loci (QTLs) influencing ADHD. 3. To test competing explanations for the association between RD and ADHD using genetic and neuropsychological analyses. 4. To examine the rates and etiology of other psychiatric correlates of RD and ADHD.